Conventionally, as an illuminating apparatus for use in image reading apparatuses and so on, a linear illuminating apparatus has been implemented by using, as a light guide member, a transparent bar having a light emitting surface which is a convex curved one, by disposing an optical diffusion region in a flat surface which is opposite to the above-mentioned curved surface, and by further placing LED elements in both end portions of the transparent bar (for example, refer to patent reference 1).
Light emitted from the illuminating apparatus having this structure can illuminate the inside of a predetermined region with uniform intensity of illumination.
Patent reference 1: JP, 2002-232648, A